Signaling system



VEZtaye ,acmss office efuei Wnent I J y 9 J. RADCLIFF 1,965,711

SIGNALING SYSTEM Filed Aug. 26. 1932 Z'z' 2 j INYENTOR Jll adclzfi' ATTORNEY Patented July 1 0, 1934 PATENT OFFICE SIGNALING SYSTEM John P. Radclifl, New York, N. Y;, assignor to American Telephone and Telegraph Company, a corporation of New York Application August 26, 1932, Serial No. 630,597 3 Claims. (01 179-16) This invention is peculiarly adapted for use inconnection with subscribers lines in which a rela-' tively low insulation resistance exists between .wires. Such lines may be described as leaky lines. These lines may be either pole lines or cable lines. The relativelylow insulation resistance between the wires may be caused by defects in the insulation or by changes in weather conditions, for example, from dry to wet weather.

One of the objects of this invention is to provide a relay device controlled by direct current impulses over a line which ,will operate over a range of leakage resistance values as long as the leakage resistance of the line is not less than a predetermined minimum. Furthermore no adjustment is necessary to maintain the arrangements of this invention in an operating condition when variation in the leakage resistance takes place so long as this quantity remains greater thana predetermined value.

Dial signals are sent over a subscriber's line by'the alternate opening and closing of the loop at the subscriber's subset by means of a dial. Whenever the dial is in such a position as to cause a short circuit to be applied to the line, a current flows over the line and the result of this flow-of current is a potential drop across a certain portion of the circuit which will hereinafter be referred to as R and which is in series with the subscriber's line and the battery. When the dial is in such a position as to cause an open circuit on the line, no current should flow through the circuit and there shorild be no potential drop' across R. However, if the insulation resistance It is proposed in this invention to apply a gas-.

filled tube of the proper type and design to perform certain necessary functions when connected to or associated with that portionv of the circuit designated as R. This gas-filled tube is of such a type and design that for any given condition of the circuit with which it is associated it will operate when a certain potential is applied from anode to cathode and will release when this applied potential has fallen to a lower value. A discharge tube suitable for use in the arrangements of the invention might,- for example, be one filled with a gas such as argon orhelium.

The invention may be more fully understood from the following description, together with the accompanying drawing in the Figures 1 and 2 of which the invention is illustrated. Fig. 1 is a circuit diagram embodyinga preferred form of the invention. Fi 2 shows graphically certain principles of operation of the arrangements.

The circuit shown in the drawing consists essentially of a gas-filled tube T which together with relay S, is associated with resistance R. Resistance R is connected in series with the subscriber's line which for the purpose of this invention description is illustrated as a T network comprising resistances Ra, R4 and R5. Battery B1 supplies the potential which is interrupted by the dial D located at the subscriber's subset. The resultant pulses of current flow through resistance R and the potential drop across'the resistance is a function of the position of the dial D.

Let R0 be the effective resistance of the line circuit between points 1 and 2 when the contacts of dial D are opened. Rd is the eflective resistance of the line circuit between points 1 and 2' when the contacts of dial D are closed. The T network which is used to represent the line circuit is composed of resistances R1, R4 and R5. Reducing the network resistances to R0 and Rc,

r'he potential from the anode to the cathode 1 .of tube T is the potential drop across the resistance R less any potential drop in R: and the winding of relay S if the tube is operated and current flows in the anode circuit. R2 is a protective resistance necessary to limit the anode current to a safe value. Relay Sis a means of transmitting the received and detected pulses to the selecting equipment of the central ofllce. The gas-filled tube circuit is 2 so adjusted that the tube will operate when the potential drop across resistance R is equal to or greater than Ea and the tube will release when the potential drop across resistance R is less than E0. The point of operation and release can be adjusted by varying resistance R and battery B2. The potential 1%!) orbattery B2 is applied to the grid of the tube .through the protective resistance R0. The purpose oi. this resistance is to limit the current' which the grid may draw when the tube is op- 5 erated.

E0 is the potential drop across resistance R when the contacts of dial D are opened. Es is the potential drop across resistance B when the contacts of dial D are closed. Let E represent the voltage 0! battery B1 which is assumed. to

be constant. Then:

E,,=E =E R Rm (4) R +R.) From these formulas, it is evident that E0 will always be less than Ec, since it was demonstrated above that R0, was always greater than'R.-

V .Now for any given subscriber's line and battery, the value or resistance R and the potential applied to the grid of tube T by battery B: may be so adjusted that the tube will operate when a' potential Ec is applied to the anode, but will release when the potential falls to the smaller value 'Eo. Furthermore since the line resistance which is represented by R4 and Rs remains essentially constant and since the leakage resistmice which is represented byR; may vary, as the leakage resistance increases E0 will decrease in value as can be seen by an inspection of,

Equation (3). Thus the tube will quench for all values of R3 above a certain minimum leak- 85- age. Let Eo(max.) be the value of potential which results across resistance R when the leakage resistance is a minimum.

Considering Equation (4) it is evident that as the-leakage resistance R: reaches a maximum [40" value, Ee will reach a minimum value given by Equation (5).

. I j Y R m The sum (Rs-l-Rs) is the resistance value of the subscriber's line circuit.

,. Hence it for any given line and battery, the

value of (the resistance R and the potential applied to the grid of the tube T are so adjusted as rto cause'the tube to operate when a voltage Ecunln.) is applied across resistance R and cause 7 the tube to releasewhen a voltage Eofinax.) is applied across resistance R, then the. tube will continue to iunction for all values oi leakage resistance above the minimum value.

'Pig. 2 illustrates graphically the improvement of this invention over the type of relay equipment which it replaces. Curve A gives the voltage available for use by the oflice equipment m: when'the dial contacts are closed. This voltage isreasonably constant in value since the leakage resistance does not aflect the loop resistance to great extent. Curve B gives the voltage which is present across the oflice equipment due to the leakage resistance of the line. Voltage 1- is required to operate the 'oiiice equipment which-may be either of the relay type or the gasfilled tube type. Voltage 3 isthe voltage below which it isneces'sary to go before the relay type orequipment will release; whereas voltage 2 is the voltage below which it is necessary to go before gas-filled tube type ofequivment will 'It can'be seen from the',g roup of curves that the gas tube equipment can be employed on-lines'inwhichthe resistance is inimh lower than those lines which employ relay equipment. While the invention has been disclosed as embodied in a specific .torm, it will be understood that it is capable of embodiment in other and different forms without departing from the spirit and scope of the invention. For example, the use of a gas-filled tube having a greater or smaller number of elements shall not be construed as departing in sense from the embodiment of the invention described herein for the purpose of illustration when read in connection with the accompanying drawing and for which the appended claims are drawn. Furthermore, although the tube used to describe this invention is of the hot cathode type, it is understood that a gas-filled tube of the cold cathode type may be employed in this invention without departing from the spirit and scope of the invention.

What is claimed is:

1. A marginal relay circuit comprising a line having series resistance and shunt leakage resistance, a source of potential in said line, switching means i'or applying an open or short circuit condition at one end 01' said line, a terminating resistance bridged across the other end of said line, a gas-filled discharge tube having its discharge path bridged across said terminating resistance, the value oi said terminating resistance. being so chosen that the voltage across said terminating resistance due to said source of potential will always be less than the breakdown voltage of said tube when the remote end of said line is open circuited and will always be greater than the breakdown voltage of said tube when the remote end of the line is short circuited. 2. A marginal relaycircuit comprising a line having series resistance and shunt leakage resistance, a source of potential in said line, switching means for applying an open or short circuit condition at one end of said line, a terminating resistance bridged across the other end of said line. a gas-filled discharge tube having its discharge-path bridged across said terminating 2 resistance, the value of said terminating resistance and the constants of said tube circuit being so chosen that the voltage across said terminating resistance due to said source 01' potential when the remote endof said line is open cir- 135 cuited will be below the breakdown voltage or said tube and will always be less than the voltage across said resistance when the remote end of said line is closed, which latter voltage will be greater than the breakdown voltage of said tube. 130

3. A marginal relay circuit comprising a line having series resistance and shunt leakage resistance, a source of potential in said line, switching means for applying an open or short circuit condition at one end of said line, a terminating'resistance bridged across the other end of said line, a gas-filled discharge tube having its discharge path bridged across said terminating resistance, the value of said terminating resistance and the constants said tube circuit being so chosen with respect to said line and 'said source oi. potential therein that said tube will not be operated by voltages across said terminating resistance resulting from leakage re-. sistance of an arbitrary minimum value across said line but will be operated by voltages across said terminating resistance whenever said line has a short circuited condition at the end thereof.

JOHNP. 

